Field of the Invention
The present invention relates to apparatuses, systems, and methods for sensing or measuring chemical components or constituents (e.g., analytes) in the breath of a patient or “subject,” and preferably endogenous analytes in breath, and correspondingly, to devices and methods for regulating the flow of the breath sample during the pre-measurement capture process and/or during such sensing or measurement.
Description of the Related Art
The importance or benefits of measuring the presence or concentration of chemical constituents in the body to aid in assessing a patient or subject's physiological or pathophysiological state is well known in the medical and diagnostic communities. Standard approaches to chemically-based diagnostic screening and analysis typically involve blood tests and urine tests.
Blood tests of course require that blood be drawn. Patients associate this procedure with pain, a factor that can have adverse implications for patient compliance in home-based assessments. In clinical settings, the need to draw blood typically requires trained personnel to draw the blood, carefully and properly label it, handle it and the like. It is typically necessary to transport the sample to a laboratory, often off site, for analysis. Given the logistics and economics, the lab analysis usually is carried out in bulk on large numbers of samples, thus requiring bulk handling and logistics considerations and introducing delay into the time required to obtain results. It is then typically necessary for follow-up analysis by the physician or clinician to assess the lab results and further communicate with the patient. In large part because of these logistics and delays, it is usually necessary for the patient or subject to return for a follow up visit, thus taking additional clinical time and causing additional expense.
Urine tests involve similar drawbacks. Such tests can be messy, unsanitary, and introduce issues with respect to labeling, handling and contamination avoidance. They also usually involve lab analysis, with associated delays and expense. As with blood, urine tests, it is typically necessary to transport the samples to an off-site laboratory for analysis. Given the logistics, the lab analysis usually is carried out in bulk on large numbers of samples, thus again involving delay and expense.
There are many instances in which it is desirable to sense the presence and/or quantity or concentration of an analyte in a gas. “Analyte” as the term is used herein is used broadly to mean the chemical component or constituent that is sought to be sensed using devices and methods according to various aspects of the invention. An analyte may be or comprise an element, compound or other molecule, an ion or molecular fragment, or other substance that may be contained within a fluid. In some instances, embodiments and methods, there may be more than one analyte present, and an objective is to sense multiple analytes. “Gas” as the term is used herein also is used broadly and according to its common meaning to include not only pure gas phases but also vapors, non-liquid fluid phases, gaseous colloidal suspensions, solid phase particulate matter or liquid phase droplets entrained or suspended in gases or vapors, and the like. “Sense” and “sensing” as the terms are used herein are used broadly to mean detecting the presence of one or more analytes, or to measure the amount or concentration of the one or more analytes.
The use of breath as a source of chemical analysis can overcome many of these drawbacks. The presence of these analytes in breath and their associated correlations with physiological or pathophysiological states offer the substantial theoretical or potential benefit of providing information about the underlying or correlated physiological or pathophysiological state of the subject, in some cases enabling one to screen, diagnose and/or treat a patient or subject easily and cost effectively. Breath analysis can avoid painful invasive techniques such as with blood tests, and messy and cumbersome techniques such as urine analysis. Moreover, in many applications test results can be obtained promptly, e.g., during a single typical patient exam or office visit, and cost effectively.
As is well known in the field of pulmonology, breath, and particularly breath exhalations, comprise a range of chemical components, or analytes. An “analyte” is a chemical component or constituent that is a candidate for sensing, detection or measurement. Breath composition varies somewhat from subject to subject, and within a given subject, from time to time, depending on such factors as physical condition (e.g., weight, body composition), diet (e.g., general diet, recent intake of food, liquids, etc.), exertion level (e.g., resting metabolic rate versus under stress or exercise), and pathology (e.g., diseased state). Approximately 200 to 300 analytes can be found in human breath.
Certain breath analytes have been correlated with specific physiological or pathophysiological states. Such correlations are particularly useful for “endogenous” analytes (i.e., those that are produced by the body), as opposed to “exogenous” analytes (i.e., those that are present in breath strictly as a result of inhalation, ingestion or consumption and subsequent exhalation by the subject). Examples are set forth in Table 1.
TABLE 1Candidate AnalyteIllustrative Pathophysiology/Physical StateAcetoneLipid metabolism (e.g., epilepsy management, nutritionalmonitoring, weight loss therapy, early warning of diabeticketoacidosis), environmental monitoring, acetone toxicity,congestive heart failure, malnutrition, exercise, management ofeating disordersEthanolAlcohol toxicity, bacterial growthAcetaldehydeAmmoniaLiver or renal failure, protein metabolism, dialysis monitoring,early detection of chronic kidney disease, acute kidney diseasedetection and managementOxygen and CarbonResting metabolic rate, respiratory quotient, oxygen uptakeDioxideIsopreneLung injury, cholesterol synthesis, smoking damagePentaneLipid peroxidation (breast cancer, transplant rejection),oxidative tissue damage, asthma, smoking damage, chronicobstructive pulmonary disease (“COPD”)EthaneSmoking damage, lipid peroxidation, asthma, COPDAlkanesLung disease, cancer metabolic markersBenzeneCancer metabolic monitorsCarbon-13H. pylori infectionMethanolIngestion, bacterial floraLeukotrienesPresent in breath condensate, cancer markersHydrogen peroxidePresent in breath condensateIsoprostanePresent in breath condensate, cancer markersPeroxynitritePresent in breath condensateCytokinesPresent in breath condensateGlycansGlucose measurement, metabolic anomalies (e.g., collectedfrom cellular debris)Carbon monoxideInflammation in airway (asthma, bronchiesctasis), lung diseaseChloroformDichlorobenzeneCompromised pulmonary functionTrimethyl amineUremiaDimethyl amineUremiaDiethyl amineIntestinal bacteriaMethanethiolIntestinal bacteriaMethylethylketoneLipid metabolismO-toluidineCancer markerPentane sulfidesLipid peroxidationHydrogen sulfideDental disease, ovulationSulfated hydrocarbonCirrhosisCannabisDrug concentrationG-HBADrug testingNitric oxideInflammation, lung diseasePropaneProtein oxidation, lung diseaseButaneProtein oxidation, lung diseaseOther Ketones (otherLipid metabolismthan acetone)Ethyl mercaptaneCirrhosisDimethyl sulfideCirrhosisDimethyl disulfideCirrhosisCarbon disulfideSchizophrenia3-heptanonePropionic acidaemia7-methyl tridecaneLung cancerNonaneBreast cancer5-methyl tridecaneBreast cancer3-methyl undecaneBreast cancer6-methyl pentadecaneBreast cancer3-methyl propanoneBreast cancer3-methyl nonadecaneBreast cancer4-methyl dodecaneBreast cancer2-methyl octaneBreast cancerTrichloroethane2-butanoneEthyl benzeneXylene (M, P, O)StyreneTetrachloroetheneTolueneEthyleneHydrogen
The inherent relative advantage of breath analysis over other techniques, together with the relatively wide array of analytes and analyte correlations, illustrate that the potential benefits breath analysis offers are substantial.
Notwithstanding these potential benefits, however, with the exception of breath ethanol devices used for law enforcement, there has been a paucity of breath analyzers on the commercial market, particularly in medically-related applications. This lack of commercialization is attributable in large measure to the relatively substantial technical and practical challenges associated with the technology. Principal among them is the requirement for sensitivity. Analytes of interest, particularly endogenous analytes, often are present in extremely low concentrations, e.g., of only parts per million (“ppm”) or parts per billion (“ppb”). In addition, the requirements for discrimination or selectivity is of critical concern. As noted herein above, breath typically includes a large number, sometimes hundreds, of chemical components in a complex matrix. Breath also usually has considerable moisture content. Chemical sensing regimes conducive for breath ammonia measurement, for example, are preferably sensitive to 50 ppb in the presence of 3 to 6% water vapor with 3 to 5% carbon dioxide. Successfully and reliably sensing a particular analyte in such a heterogeneous and chemically-reactive environment presents substantial challenges.
Most publicly-known breath analysis devices and methods involve using a single breath, and more specifically a single exhalation, as the breath sample to identify or measure a single analyte. The sample is collected and analyzed to determine whether the analyte is present, and in some cases, to measure its concentration. The breath analysis system introduced by Abbott Laboratories, e.g., in U.S. Pat. Nos. 4,970,172, 5,071,769, and 5,174,959, provides an illustrative example. There, Abbott used a single exhalation from a patient to detect the presence of acetone to obtain information about fat metabolism.
Notwithstanding the potential benefits of breath analysis, particularly portable breath analysis devices for home or field use, commercial offerings of such devices have been available only recently, and the accuracy and reliability in such settings have left much room for improvement. Practical breath analysis devices must operate accurately and reliably in the context of their use, e.g., in patient homes, clinics, etc., in varying environments, (temperatures, humidity, etc.), with various types of patients, over the life of the devices.
The use of multiple breaths is substantially lesser known and studied. Published reports generally have been limited to the determination of the production rate of carbon dioxide and the consumption rate of oxygen. This technique was developed due to the presence of these two analytes (oxygen and carbon dioxide) in the ambient atmosphere.
These approaches have been limited and relatively deficient, however, for example, in that the breath sample or samples are collected in bulk, so that the analyte of interest is mixed in with other constituents. This often dilutes the analyte and increases the difficulty of discriminating the desired analyte. These approaches also limit the flexibility of the breath analysis to undertake more specialized or complex analyses.
Additionally, such approaches are relatively deficient because the instrumentation used for single breath analysis usually is different from and sometimes inadequate for multiple breath analyte measurement.
Yet another challenge to breath analysis involves the fluid mechanical properties of the breath sample as it travels through the measurement device.
There is considerable advantage in providing breath analysis devices that can accurately and reliably sense or measure breath analytes in a clinical or patient home setting. Thus, there is a need for small or portable, cost effective devices and components.
In many instances, there is a need or it is desirable to make the analysis for an analyte in the field, or otherwise to make such assessment without a requirement for expensive and cumbersome support equipment such as would be available in a hospital, laboratory or test facility. It is often desirable to do so in some cases with a largely self-contained device, preferably portable, and often preferably easy to use. It also is necessary or desirable in some instances to have the capability to sense the analyte in the fluid stream in real time or near real time. In addition, and as a general matter, it is highly desirable to accomplish such sensing accurately and reliably.
The background matrix of breath presents numerous challenges to sensing systems, which necessitate complex processing steps and which further preclude system integration into a form factor suitable for portable usage by layman end-users. For example, breath contains high levels of humidity and moisture, which may interfere with the sensor or cause condensation within the portable device, amongst other concerns. Also, the flow rate or pressure of breath as it is collected from a user typically varies quite considerably. Flow rate variations are known to impact, often significantly, the response of chemical sensors. Breath, especially when directly collected from a user, is typically at or near core body temperature, which may be considerably different than the ambient temperature. Additionally, body temperature may vary from user to user or from day to day, even for a single user. Devising a breath analyzer thus is a non-trivial task, made all the more difficult to extent one tries to design and portable and field-amenable device.
Notably, the measurement of endogenous analytes in breath presents different challenges and requires different techniques and devices than the measurement of exogenous analytes. Endogenous analytes are those that are produced by the body, excluding the lumen of the gastrointestinal tract, whereas exogenous analytes are those that are present in breath as a result of the outside influence or as a result of user consumption. However, many analytes are produced endogenously and can also be exogenously introduced. For example, ammonia is produced endogenously through the metabolism of amino acids, but can also be introduced exogenously from the environment such as ammonia-containing household cleaning supplies. The term “endogenous” is used according to its common meaning within the field. Endogenous analytes are produced by natural or unnatural means within the human body, its tissues or organs, typically excluding the lumen of the gastrointestinal tract.
There are a number of significant challenges to measuring endogenous analytes in breath. Endogenous analytes typically have significantly lower concentrations in the breath, often on the order of parts per million (“ppm”), parts per billion (“ppb”), or less. Additionally, measurement of endogenous analytes requires discrimination of the analyte in a complex matrix of background gases. Instead of typical atmospheric gas composition (e.g., primarily nitrogen), exhaled breath has high humidity content and larger carbon dioxide concentration. This leads to unique challenges in chemical sensitivity, selectivity and stability. For example, chemistries conducive for breath ammonia measurement are preferably sensitive to 50 ppb in the presence of 3 to 6% water vapor with 3 to 5% carbon dioxide.
Because of the historical difficulty in even detecting endogenous breath analytes, other challenges have not been extensively investigated. Examples of such challenges include: (a) correlating the analytes to health or disease states, (b) measuring these analytes given characteristics of human exhalation, e.g., flow rate and expiratory pressure, (c) measuring these analytes sensitively and selectively, and (d) doing all these in a portable, cost effective package that can be implemented in medical or home settings.
Colorimetric devices are one method for measuring a reaction involving a breath analyte. Colorimetric approaches to endogenous breath analysis have historically been plagued with lengthy response times, and expensive components. Often such analysis has to be performed in a laboratory. Thus there remains a need for a breath analyzer that can measure endogenous breath components present in relatively low concentrations, such as acetone, accurately and quickly, without a long wait period for results, in addition to being inexpensive and useable by the layperson. It is also preferable if the breath analyzer is capable of measuring multiple analytes.